Table 2 shows some examples of coverage by the Illumina 610 Quad microarray for ten genes that are of particular interest. We chose this array because it offers a median level of coverage among the seven arrays we studied. These genes were among the most highly prioritized by the addiction researchers with whom we consulted. The selection process involved a number of criteria, including pharmacogenetic pathways, gene expression data, and mouse models. For example, CDH13 (Cadherin 13) is known to be expressed in neurons in the human adult cerebral cortex, midbrain, thalamus and medulla regions [5]. Because it is also known to inhibit neurite extension [6] and activate a number of signaling pathways [7]–[10], it is a strong candidate for the genetic study of addiction phenotypes [11]. CDH13 contains 2,414 SNPs that are common in the African population, and only 50% of these are tagged by the by the Illumina 610 Quad microarray. Figure S1 shows the complete distribution of individual gene coverage percentages using our primary set of 910 genes for the Illumina 610 Quad microarray in each population.
